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Voice Over IP Using SIP

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VoIP in the Enterprise • Services available to all company’s users, on-site, offsite and multi-site – toll bypass. • No telephone line required for home-workers and remote offices. • Single infrastructure for data and voice. • Effectiveness tools. • Service operation can be outsourced in a Centrex-like manner (MCI Advantage). Like with web/email, single server may host multiple domains. iLabs Voice Over IP Using SIP

Example: this is an entry in the sip.ilabs.interop.net domain _sip._udp.asterisk in SRV 10 10 5060 asterisk.sip.ilabs.interop.net. A SIP endpoint will query DNS to find a SIP server for call setup to a SIP URI SIP uses DNS to Find Addresses A SIP URI: sip:17005553171@asterisk.sip.ilabs.interop.net SRV records in DNS are used to find SIP services: _sip._udp.domain in SRV <priority> <weight> <port> server Prepend server dns name with _sip and _IP transport priority - lower numbers are chosen first With multiple SRV records of different priority the lowest numbered server will be tried first weight - higher numbered entries get more connects With multiple SRV records of same priority, more connects will go to servers with higher weights iLabs Voice Over IP Using SIP

The top-level domain e164.arpa is used like in-addr.arpa. A phone number like 17025553171 will have an NAPTR entry for 1.7.1.3.5.5.5.2.0.7.1.e164.arpa: 1.7.1.3.5.5.5.2.0.7.1.e164.arpa in a naptr 1 10 “s” “SIP+D2U” “” “sip:crw@transcendental.com” A SIP endpoint will query DNS to find a SIP server for call setup to a telephone number E.164 is the ITU standard for telephone numbering. ENUM is the the RFC standard for mapping telephone numbers into DNS. ENUM Maps Telephone Numbers into DNS A telephone number: +1 702 555 3171 Flags and Service fields are typically fixed for SIP entries NAPTR records in DNS are used to find SIP URIs for telephone numbers: domain in a NAPTR <order> <pref> “s” “SIP+D2U” <regexp> <target> Target SIP URI which may be static, or composed from domain using regex expression order in which records are read, looking for a match in capability preference - lower numbers are chosen first With multiple NAPTR records of the same order, the lowest number will be tried first. May be overriden to select transport. Regular expression used to do substitution from domain into target string iLabs Voice Over IP Using SIP

SIP Servers Perform Call Setup • SIP Registrar • accept registration requests from users • maintains user’s whereabouts at a Location Server (like GSM HLR) • SIP Proxy Server • relays call signaling, i.e. acts as both client and server • operates in a transactional manner, i.e., it keeps no session state • transparent to end-devices • does not generate messages on its own (except ACK and CANCEL) • allows for additional services (call forwarding, AAA, forking, etc.) • SIP Redirect Server • redirects callers to other servers • Used rather rarely as operators appreciate staying in communication path. May be used to achieve very scalable load distribution. These are logical functions and are usually on the same server iLabs Voice Over IP Using SIP

A SIP Registrar Helps Mobility A SIP registrar keeps track of users’ whereabouts. This registration example establishes presence of user with address for one hour and binds this address to user’s current location Location database SIP Registrar Registering is not logging in. It is optional. An unregisterd device can still make calls. REGISTER sip:sip.ilabs.interop.net SIP/2.0 From: sip:crw@sip.ilabs.interop.net To: sip:crw@sip.ilabs.interop.net Contact:<sip:45.210.3.78> Expires: 3600 iLabs Voice Over IP Using SIP

Summary of SIP Properties • Textual (HTTP-like) client-server protocol • – Easy to debug, extend and process with textual operating systems • End-to-end • It puts most intelligence into end-devices (“user agents”) – good for scalability and extensibility • The network infrastructure designed to be lightweight. Network functionality (registrar, proxy) are typically logical parts of a single server. • Internet addressing using URIs • – E.g., sip:crw@transcendental.com • – Non-SIP URIs possible to (e.g., they may be used to redirect a caller to webpage) • – Address space unlimited and may be used to create services (sip:sales@hotel.xy; geo.position:=48.54_-123.84_120) • It delivers mobility: User can register from one or more locations with IP connectivity iLabs Voice Over IP Using SIP

What SIP is Not • Transport • QoS Reservation Protocol • Gateway Control Protocol • Some argue it may be used for accessing IP-enabled appliances ... • It does NOT dictate ... • Product features and services (color of your phone and distinctive ringing melodies, number of simultaneous calls your phone can handle, don’t disturb feature, ...) • Network configuration iLabs Voice Over IP Using SIP

What are Enterprise Features? • Things you can do with a traditional PBX and a proprietary phone with lots of extra buttons on it: • Call forward (set your phone to always forward to another; many variants such as call forward on busy, etc) • Call waiting (be notified when another call comes in, be able to pick up and switch between two calls) • Message Waiting Indicator (implies voicemail) • DTMF (touch tones to drive automated menu systems) • Call transfer, attended (you initiate transfer, talk privately with new party, then connect the two and leave the call) • Call transfer, blind (you initiate transfer, hang up) • Hold/resume with music See the Internet Draft “Session Initiation Protocol Service Examples”, at http://www.ietf.org/internet-drafts/draft-ietf-sipping-service-examples-08.txt iLabs Voice Over IP Using SIP

What We Learned in the iLabs • SIP is naturally interoperable • SIP is easy to debug, and basic call interoperability is good • All phones are not created equal • Tremendous differences between phones in technical factors such as voice quality, performance, handling of jitter, configurability etc, as well as human factors such as how it feels and sounds • Getting started is easy • We had phones working by lunch of the first day and many of them worked the first time • Enterprise features are tough • What’s easy for a PBX must be reinvented with SIP ... it’s a moving target • For features you care about, test, test, test! iLabs Voice Over IP Using SIP

What You Can Do in the iLabs • Call from any phone to any other phone - play with different phones! Play with enterprise features!! • Call to the PSTN - call your office and talk to someone • Use three different video phones • Use three different WiFi phones • Use a protocol analyzer to watch and listen to SIP traffic • Make Elvis dance! • Find out what your cell phone number spells iLabs Voice Over IP Using SIP

How to Learn More • Come see the iLabs SIP demo and ask questions • Pick up these white papers in the iLabs or electronically: • What is SIP?  SIP, Firewalls and Security • What is ENUM?  SIP and the PSTN • Getting Started with SIP  SIP Resources • Migrating to SIP • http://www.ilabs.interop.net • iLabs white papers, vendor white papers, Network World articles, diagrams, team bios and vendor links, this presentation • http://www.opus1.com/sip • iLabs white papers, this presentation and layout diagram (up forever) iLabs Voice Over IP Using SIP